You don't trademark a cartoon character (or anything else for that matter) unless YOU USE IT IN TRADE.
If you just create it and never use it commercially as a trade mark, then its not a trade mark, so how can you trademark something that is not a mark used in trade? In fact, if you use something, like a motto for your business, and consider it a trademark, but then you stop using it for a few years, you can lose the right to it, especially if other businesses use the same thing and you do not defend your right to it, that also can cause you to lose your right to it.
Copyright applies to the artwork of it though. And that is pretty much automatic. I wouldn't waste money REGISTERING the copyright of every cartoon you draw, unless you expect to develope something to be really big, popular and visible. That's the problem I find with young artists. SO paranoid that something they draw will somehow be stolen and become "the next big thing". It just doesn't work that way though. There's alot more to making millions than just drawing a cartoon character.